As the energy crisis continues, the use of coal gains in importance. It is generally agreed by industry that tremendous coal reserves are available, leaving the more prominent problems of transportation and handling to be solved.
The equipment in which coal is burned has been steadily improved from the old locomotive where shovelfuls of the solid fuel were pitched onto a grate where the heat of combustion rose to the bottom of a water boiler. Coal is now controlled in its particle size by highly sophisticated mills and is air-transported through conduits and discharged from nozzles into zones of combustion. At present, development has concentrated on burning crushed coal in a bed supported by a horizontally extended perforated structure up through which combustion air is forced. The problems of introducing the crushed solid fuel into the bed fluidized above the perforated support are paralleled by the innovations in the system for removing solid residue from the zone of cumbustion.
Beyond the problems of fuel flow into the bed, and ash removal from the bed, is the problem of inhibiting discharge of sulfur and nitrogen compounds with the gaseous products of combustion. There are many different approaches to the control of these environment-threatening substances, and the control of the maximum temperature of the fluidized bed in combustion is a significant factor. In general, the present problems revolve around maintaining a heat exchanger in contact with the upper portion of the bed to maintain temperature control.
Establishing the reaches of a tubular heat exchanger within the upper portion of the bed for its temperature control, may appear to be a simple problem. The vertical banks of heat exchanger tube reaches are to be supported in their longitudinal extension within the bed. The vertical banks of tubes may be horizontally spaced from each other at distances which will not interfere with the fluidizing of the combusting bed. The present problem is how to support these vertical banks of horizontal reaches by a structure which extends up from the perforated bed support. This support for the heat exchanger is exposed to the high temperature of the bed and, therefore, this temperature must be controlled to prevent thermal distortion and deterioration of the support.